Machine tool



June 14, 1949. "F. H. BOGARTQ' 2,473,133

v MACHINE TOOL Filed Dec. 11, 1946 Y 3 Sheets-Sheet 1 INVENTOR. FREDl'LBugHRT I I Fh'ruRNEy June 14, 1949; v F. H. BOGART 3 MACHINE TOOLFiled Dec. 11, 1946 3 Sheets-Sheet 2 I N VEN TOR.

FRED I-LEugHR T HT'I'DHNEYS F. H. BOGART MACHINE TOOL June 14, 1949.

Filed Dec.

3 Sheets-Sheetfi I INVENTOR. FRIED H.EUHFIRT Patented June 14, 1949UNITED STATES PATENT OFFICE Fred .H. Bogart, South Euclid, Ohio,assignor to The Warner & Swasey Company, Cleveland, Ohio, acorporationof Ohio Application December 11, 19.46,.Serial No. 715,356

--effective to transmit a substantially constant torque throughout theuseful life of the friction members.

Anotherobject of the invention is to provide .an improved means formaintaining a friction zclutch engaged:with a substantially constantpredetermined pressure, the means being so constructedvand arranged asto be adjustable to permit selection of theclutch-engaging pressure-and,tO automatically compensate for wear-of the friction members of theclutch.

A'further object oftheinvention is to provide an improved means foremploying a spring to maintain a friction :clutch in engagement, themeans being so constructed :and :arranged I that the Wear of thefriction members of-the clutch, rresultingin reduced force of thespring, willnot effect the pressure with which :th'e-clutch isen-,gaged.

A-still further object of the invention is the provision of an improved"mechanism for maintainingthe friction members of a friction clutch inengagement :under substantiallyuniform pressure, :the mechanismincluding a lever means and a spring acting thereon in a'manner suchthat the decrease in force of thespringdue to wear of the frictionmembers of the clutch, is com- ..pensated by an/increase in mechanicaladvantage of the levermeans.

A more specificobject of the invention is'to provide an improvedfriction clutch for use in machine tools or the like and comprising an-improved 511162115 for maintaining the friction clutch. in engagementunder :a selected substantially uniformforce; the said means comprisinga standardorzmain spring acting througha lever :means for effectingengagementof the clutch, and an adjustable ireaction spring also :acting"upon the lever means bntiin opposition to the standard or mainspring'to provide a 'rangeof clutch-engagingpressures,;the springs andlover :means being: so constructed 'and arranged :as: to automaticallycompensate for wear 'of' the friction members of therclutch'zsothatiwhen adjusted "2 for a selected clutch-engaging pressure, thatpressure will be maintained substantially-constant.

A still more specific object of the invention is to provide an improvedmeans for maintaining a friction clutch engaged with asubstantiallyconstant predetermined pressure, the means including-athree-armpivoted-lever with one arm connected to the'clutch forengaging-the'latter, -a spring acting upon each of the other arms of thelever one spring actingin a direction to-exert -clutch-engaging pressureand the other "spring acting in opposition thereto, the last-mentioned:s-pring :being provided with means tovary "its force :wherebytheresulting clutch+engaging pressure may be adjusted to a selected value;the

lever and springs beingso constructed and arranged that when the formerrocks about its ipivot, due to wear "of the friction members of theclutch, the effective values of .the lever arms upon which thesprings-act will respectivelyincrease :and decrease as the forces of thecorresponding .springs respectively decrease and increase, :vvherebythevproduct ofthe force of-each spring by the corresponding effectiveleverarm remains substantially constant.

.Another object of the invention is to provide a machine tool having awork-gripping means including :movable jaws, a wrench spindle for-moving said jawsto'and fromwork-gripping position, power driven means,and anoperative con- :nection including a friction clutch between thepower driven means and the-wrench spindle,'with an improved'means formaintaining the friction aclutch engagedunder a substantially constantpredetermined pressure; the improved means be- :ing so constructedandarrangedas to automatically compensate for'wear of the frictionmembers of the -clu-tch whereby the torque trans- *mitted to said wrenchspindle "will remain at a substantially constant predetermined value.

An additional object-ofthe invention is toproremainsubstantially'constant even-thuogh "the friction members of the clutchshould *become Other and further-objects of the 'invention' reside invarious 'features of construction, combina- -tion and arrangements ofparts=as will-"herein- 55 after become more clearly apparent from "theable means.

3 following detailed description of the present preferred embodiment ofthe invention, described with reference to the accompanying drawingswherein:

Fig. 1 is a fragmentary end elevational view of the headstock of amachine tool provided with a work gripping chuck and a power operatedchuck wrench embodying the present invention;

Fig. 2 is a fragmentary view of the power operated chuck wrench unitshown in Fig. 1, the view being partly in elevation and partly insection to reveal an improved clutch engaging mechanism constructed inaccordance with this invention;

Fig. 3 is a view, partly in section and partly in end elevation, thesection being taken substantially on the line 3-3 of Fig. 2;

Fig. 4 is a sectional view taken substantially on the line 3-4' of Fig.2;

Fig. 5 is a fragmentary view, partly in section and partly in elevation,showing the mechanism for rotating the power operated chuck wrenchspindle and for axially moving the latter; and

Fig. 6 is a diagrammatic representation of the physical principlesemployed in this invention.

For the purpose of disclosing one practical embodiment or application ofthe present invention, but without limiting it thereto, the invention isherein described and illustrated as applied to the driving mechanism fora power operated chuck wrench of a machine tool. Hence, in Fig. 1 of thedrawings is shown a machine tool, of a more or less conventional type,comprising a headstock ll) mounted upon a base II and provided with theusual chuck 12 which is connected with the work spindle in theconventional manner. This chuck is of the type having mechanismcontained therein for actuating the jaws 12a, the

' mechanism being operated by a rotatable member insertable into asuitably shaped opening 13 of which one or more may be provided atsuitably spaced points about the periphery of the chuck, only one beinghere indicated. This mechanism is conventional and hence need not bedescribed in detail.

Adjacent the chuck l2, and preferably to the rear thereof, as viewedfrom the front of the .machine, i. e., from the left of Fig. 1, there ismounted a power operated chuck wrench unit,

generally designated M, which may be attached to the headstock of themachine tool by any suit- This power operated chuck wrench unitcomprises a rotatable member or wrench spindle E5, the outer end ofwhich may be polygonally shaped or provided with spaced ears IG forengagement with correspondingly shaped recesses in an operating memberlocated in the opening 53 of the chuck, the engagement being supportedwithin suitable bosses provided in the housing H of the chuck wrenchunit [4, and a .lost motion disk 18 is splined or otherwise slid- .ablyconnected with a portion of the wrench ,spindle, the disk beingrestrained from axial movement with the wrench spindle by any suit-.able means. As will be seen from Figs. 3 and 5,

the wrench member or spindle 15 extends through a collar-like extension49 of a worm gear 20, the extension l9 being journaled within a suitablecylindrical portion or boss 2| of the housing H.

The inner periphery of the collar portion I9 is .provided with aninwardly extending lug 22,v

which is adapted to cooperate with an outwardly extending lug 23provided upon the lost motion disk l8, the construction being such thatrotation of the worm wheel 26 will effect rotation of the disk is andthereby the wrench member I5 when the abutments or extensions 22 and 23are in engagement. When the worm wheel 28 is rotated in a direction tomove the said abutments out of engagement, the said worm wheel may makenearly a complete revolution before again engaging the abutment 23,thereby enabling a relatively sharp blow to be applied to the latter fora purpose hereinafter described.

The wrench spindle I5 is moved axially to and from engagement with theopening G3 in the chuck I2 by means of a toothed segment 24, which isrockably mounted within the housing i! and has one set of teeth 25cooperating with a circular rack 26 provided upon the wrench spindle IS.A diametrically opposite toothed portion 21 of member 24 is engaged bythe teeth of a rack 28 which is slidable within the housing H. The rack28 is pivotally connected by link 29 to one arm of a lever 30 which ispivoted to the headstock at 31, the other arm of lever 30 beingpivotally connected with an operating plunger 32 slidably mounted upon aportion of the headstock of the machine tool. The lever 30 is providedwith an indicating arm or pointer 33 adapted to rock with the lever andcooperate with plate 34 carrying indicia for indicating the position ofthe wrench member or spindle relative to the chuck.

It will be seen that, with the parts positioned as illustrated in Figs.1 and 5, the handle or plunger 32 is located at its innermost position.and the rack 28 has therefore retracted the wrench portion of spindle Hifrom engagement with the chuck. When the handle or plunger 32 is pulledoutwardly, the pointer 33 will move to the indicia marked In on plate34, and the rack 28 will rock the toothed member 24 to thereby move thewrench portion of the wrench spindle l5 into engagement with the openingl3 of the chuck. In order that this engagement may not be eifected whenthe chuck spindle and chuck are rotating, an interlock is provided withthe main control lever 35 for the headstock mechanism. This interlockcomprises a spring pressed plunger 36 positioned to cooperate with anotch 37 in the rack 28, the spring of the plunger 35 normally tendingto withdraw the plunger from engagement with the rack, the plunger beingheld in its depressed position by cooperation with the main controllever 35 when the work spindle and chuck are being rotated, thuspreventing actuation of the rack 28.

The wrench spindle l5 of the power wrench mechanism is adapted to berotated by a reversible electric motor generally designated 38, thearmature shaft of which is connected to one set of disk plates orfriction members of a friction clutch 39. The other set of disk platesor friction members of the clutch are connected to a movable member 46of the clutch, which is splined or keyed to a worm shaft 2! journaled inthe housing IT. This shaft 4! is provided with a worm 42 whichcooperates with the previously mentioned worm wheel 20 for rotating thewrench spindle 15. The clutch herein illustrated and the mechanism aboutto be described are so constructed that the worm is continuously drivenwhenever the motor 38 is energized, the clutch disks or friction membersbeing held in continuous engagement under substantially uniform tarelespressure to produce 'a uniform torque for the "wrench spindle eventhough the'iriction members "of the clutch have become worn. Hence, thejaws of the chuck [2 may be actuated to work- -"grippin position by apredetermined force, the

lost motion connection provided by the disk I8 fand the extension collar1 9 "ofworm wheel providing a hammer-like blowfor disengaging the chuckjaws from the work gripped therein.

Engagement of the plates of the clutch iseffected bya novel'm'echanismcomprising a sleevelike member 53; which is mounted upon the mem- "ber49 for relative rotation therebetween 'byan- *tifriction means M,the'sleeve member 43 being "adapted to be axially moved to apply forceto the "disks or friction members through the agency of the movablemember 40. For effecting this axial movement of the sleeve member is itsouter surface is provided with two diametrically arranged slots forreceiving a pair of shoes as which are -pivotally carried by the outerends of a forked farm lfi provided on a pivoted force transmittinghousing ll by bearing pins 48 and a9, respectively. The illustratedmember or lever G7 is also provided with an arm '50 extending at anangle with respect to the arm 46, the outer end of arm fillbeingpreferably bifurcated and provided with a roller rotatably mountedwithin the spaced portions of the arm. The roller 5| engages a plunger52, which is-slidably positioned within a bore provided in the housingll, the plunger be- 'lllg forced outwardly of the bore by a forceexerting means here illustrated as a coiled main spring "53 havingapredetermined length and compressed to a predetermined amount by a plug54 threaded in the outer end of the bore.

It will be readilyunderstood that the spring53 yvill exert apredetermined force upon the arm .50 and thereby rock the forcetransmitting mem- *ber or lever ll to apply a predetermined forcethrough the arm 4%, shoes 45, and theintervening mechanismto thefriction members'ordisks of the clutch 39. As the friction membersbecome worn through usage, the member or lever ll will rock under actionof the spring 53 to maintain the friction members in constantengagement. This will result in elongation of the spring 53 and acorresponding reduction in the force exerted thereby. However, inaccordance with this invention this reduction in forc e exerted by thespring is compensated bya corresponding increase in mechanical advantageof the force trans- 135 imitting members or lever'means ll'so thatth'e"force exerted upon the clutch 39 remains subfs'tantially constantthroughout the useful life of internally a d externally threaded.regimen-lei threads of the plug cooperate with external threads upon a'headed member 59 disposed within the bore and forming an abutment "forthe-inner end of .a force exerting means which may comprise a coilspring fi'wsurrounding areduee'd portion of the plunger 5'l,the'-outerend of the spring 'ex'erting a force against the headedportion of the plunger.

A calibrated adjustment operating means may be provided for rotating themember 59. Such an operating means is illustrated in Figs. land 4 ascomprising a rod 6! formed integral with the member-'59, the rodextending forwardly'of the headstock, the outer end thereof projectingthrough a suitable boss or bracket 62 carried by the headstock l0 andprovided with indicia 63. This outer end of the rod 6| is preferablyprovided with a knurled knobfid which has an elon- :gated extension 65provided with an arrow 'or pointer 66 for cooperation with theiii'diciaGS.

When theknobt l is rotated, the rod6l Will cause the member 59 to moveaxially relative to the plug 58 thereby varying the compression upon thespring Bi] and hence the force exerted through the plunger '5'! uponthe'arm55. This force will act in opposition to that exerted by thespring 53, the difference between the two forces being the force whichis effective for holding the friction members of the clutchin-engagement, this value being indicatedby the positionof the pointer58 upon the indicia 63.

Theindicia'63 may-be of any desired type representative of "either theclutch-engaging pres- --sures or the gripping pressures exerted by thejawsof the chuck i Zupon thestockor'workpiece placed therein, thislatter pressure being directly related to the clutch-engaging pressure.This relationship will be readily understood byobserving that when-themember -5'9-is rotated'the'pres- "sure applied by the arm 46 to theclutch 39, for

holding ;it in engagement, is correspondingly varied. For a givenposition of member 59 the corresponding clutch-engaging pressure willpermit the chuck wrench-spindle 15 to tighten the chuck only until thepressure exerted thereby upon the workpiece balances the torque transthefriction members. The manner in which'this after.

In order to provide for adjustment of the :clutch-engaging pressurethrough a predetermined range, the force transmitting member or "levermeans M is preferably provided with a third arm 55, the outer end ofwhich is bifurcated and slidable within a bore provided in a housing l-l"under the influence of avariable force exerting 'means. This'bore ishere shown as extending f substantially parallel with the previouslymentionedbore for the plunger '52. The outer end of placement. Aswill'be seen from-the figure,'tlie 'the bore for the pl'ungerEl isthreaded and mitted by the clutch 39. When this work-gripping pressurehas been-reached, the clutch 39 will slip and hence the work-grippingpressure of the chuck may be selected or predetermined by the amount ofthe adjustment of member 59. Therefore, the calibrations or indicia 63may be,-an5:l

preferably are, expressed directly in terms of work-gripping pressures.K

As stated above, the improved mechanism operates to maintain anyselected clutch-engaging pressure substantially constant even though the"thickness of the frictionmembers of the clutch fis'effected will bemore cle'arly'e'xplained hereinis reduced by wear. The manner in whichthis is effected can be'more readily understood with reference'to Fig.6,which is a diagrammatic representation of the force transmitting memberor lever 41 and the operating principles thereof; the-full lines of thefigure representing-the position of this member or lever when thefriction membersof the clutch operated thereby are new, and the dottedlines representing the location of the memberlorlever when the frictionmembers of the clutchhave worn to a point requin'ng'rem'ember'or lever"41 is pivoted for 'rocking ab'o'fit a pointlocated at the intersectionof the "three r diagrammaticallyrepresented arms 46, 50 and5'5,screwedtherein isa hollow plug"58"whichisboth this pivot-being providedin ithe preferrediforin lines in Fig. 6 as a result of this wear.

of the apparatus by the bearing pins 48 and 49. The line of action ofthe force applied by the standard or main spring 53 upon the arm 50 isrepresented by the arrow designated 61, and the line of action of thecorresponding clutchengagin pressure, which is transmitted to the clutchby the arm 46, is represented by the arrow 68. Likewise, the line ofaction of the force exerted upon the arm 55 by the reaction spring 60,for adjusting the effective pressure exerted upon the clutch, isrepresented by the arrow 69.

It will be seen that when the friction members of the clutch are new,the arm 46 of the member or lever 41 is preferably disposed at a slightangle to a straight line passing through the pivot of the lever 41 andparallel with the lines of action 61 and 69 of springs 53 and 69. Thelength of the arm 46 and the amount of this angle are so chosen thatwhen the friction members of the clutch are substantially worn out thesaid arm will be disposed upon the other side of the abovementionedstraight line and forming an angle therewith substantially equal to theinitial angle. Hence, the effective lever arm of the force representedby the arrow 68 may be considered as remaining substantially constantthroughout the operation of the device, since the arcuate movement ofthe outer end of the arm 46 is substantially a straight line movement.

The arms 50 and 55 of the member or lever 47 are preferablysubstantially equal in length and are each disposed at an angle withrespect to the aforementioned straight line and with respect to the arm46. The lengths of the arms 50 and 55 relative to the arm 46 arepreferably such that the forces exerted thereon are transmitted with amechanical advantage. That is to say, the effective lever armscorresponding to the physical arms 50 and 55 of the lever are greaterthan the effective lever arm corresponding to the physical arm 46; theeffective lever arm being defined as the perpendicular distance betweenthe pivot of a lever and the line of action of the force acting upon thecorresponding physical arm of the lever. Thus, the efiective lever armof the physical arm 50 when the friction members of the clutch are new,is represented by the length of the dot-dash arrow 10 extendingperpendicularly with respect to the line of force 68 of the standard ormain spring 53. Also, the effective lever arm of the physical arm 55when the friction members of the clutch are new is represented by thelength of the dot-dash arrow 1! extending perpendicularly with respectto the line of action 69 of the force exerted by the reaction sprin 60.Likewise, the effective lever arm of the physical arm 46 is representedby -the length of the dot-dash arrow 12 extending center of the rockingmotion of lever 41 perpendicularly to the arrow 68, and remainssubstantially constant throughout the rocking of the lever as thefriction members of the clutch wear. Assuming that the friction membersof the clutch have now worn substantially the entire safe amount priorto replacing. the lever 41 will have rocked to the position indicated bythe dotted Throughout this rocking motion, the pressure exerted by thearm 46 upon the clutch will remain substantially constant since,although the force of the main spring 53 decreases due to elongation asthe lever rocks, the mechanical advantage of the lever hascorrespondingly increased. This increased mechanical advantage resultsfrom an increase in the effective lever arm of the arm 50, while theeffective lever arm of the arm 46 has remained substantially constant.This increased effective lever arm for the arm 50 is represented in Fig.6 by the length of dot-dash arrow 13, whereas the effective leverage armof arm 46 remains as indicated at 12. The construction of the preferredembodiment of the invention permits this action, since the said force ofthe spring 53 is applied through a plunger 52 cooperating with theroller 5| on the arm 50, the roller moving over the face of the plungeras the lever rocks, so that the direction of the force exerted by thespring remains constant, although its effective line of action may beconsidered as having shifted to the position indicated by the arrow 14.The lengths of the arms 56 and 46 of the lever and the angletherebetween are so selected that the resulting increased mechanicaladvantage will exactly compensate for the decreased force exerted by thespring; that is to say, the force of the spring multiplied by themechanical advantage of the effective lever arms remains substantiallyconstant throughout the useful life of the friction members of theclutch.

As the lever 47 rocks, as above mentioned, resulting from wear of thefriction members of the clutch, the roller 56 on the end of the arm 55will likewise move over the end of the plunger 57 further compressingthe reaction spring 60. The force exerted by this reaction spring 60continues to act in the same direction but may be considered to haveshifted its line of action from the position indicated by the arrow 69to the position indicated by the arrow I5, correspondingly decreasingthe effective lever arm of arm 55 to a value as indicated by thedot-dash arrow 16. The length of the arm 55 relative to that of arm 46and the angle therebetween are so chosen that the mechanical advantagethereof decreases as the result of this rocking motion, and thisdecreased mechanical advantage compensates for the increased forceexerted by the reaction spring 60 due to the latter being furthercompressed. In other words, for given adjustment of member 59 theresulting force exerted by the spring 60 multiplied by the mechanicaladvantage of the lever, for any position of the latter, remainssubstantially constant.

As explained above, the force of the spring 60 acts in opposition to theforce exerted by the spring 53, the member 59 being adjusted so that theresulting force exerted by the arm 46 is of such a value as to effectengagement of the clutch with a predetermined pressure. Therefore, theclutch transmits a substantially constant torque of selected value foractuating the wrench spindle so that the latter operates the jaws of thechuck [2 to provide a predetermined work-gripping pressure, the clutchslipping after this workgripping pressure has been applied. In otherwords, when the knob 64 has been adjusted to align the pointer or arrow66 with a selected calibration 63 corresponding to a desired pressure ofthe chuck jaws, the jaws will be actuated by the wrench spindle 15 toexert this work-gripping pressure each time the wrench spindle isengaged with the chuck and this pressure will always be substantiallythe same until the knob 64 is adjusted to a new setting. The wear of ther ction m m ers of the. c utch does ot a er. the. indicated,work-gripping. pressure since, the consequent rockingv of the leverdl,increasing and decreasing. respectively. they effiective. lever arms ofthe arms 50 and. 55, compensates for.v thecorresponding decrease andincrease of'the. forces exertedby the springs. .53 and 60.

They force transmitting member. orv lever. means 41- has beenillustrated as having. the arms 50 and 55 thereof of substantially thesame. length and shortr than the arm 65; Likewise, the angles betweenarms 55"and l6, and between arms 50 and 45 have been illustrated asbeing'sub'stantially equal. It will be apparent, however, that thesevalues of the lengths of the lever arms and their angular'relationshipsare not critical'and may be varied. It is only necessary thatf theproduct of thefore applied to the arms!) by the'effec tive lever a mthereof remain substantially 'constant roeai 'sssmens' the arm; that theproduct or the force appliedto the ar ss'by'the effective lever armthereef' remain substantially constant through u am ate i c em nt of thearm; and that the position and length of arm 4 6 should be sdchosenthatitsefiectiv'ef lever arm does not materially'change throu hout the rangeof movement of the arr'nl Wh le the pres n prefer emb di e oi theinvention has been disclosed in combination with a power tol ra ed "t Wen for a chine tools, "thejinvention is to be donsid ered as limited tosuch a usesince it is of general utility. for effecting transmission ofa substan:

tall m rse assess q m a evies to a" drivenmember. Furthermore; theinvention is not restric ed to theeixact details of construc tion andarrangement'of parts as illustrated and describedfbut'islimited only asrequired by the spirit and scope of appended claims.

Having thusdesjcribed' invent ng, I claim:

1. Ina chine tool 'aav nga chuck and @OW-Qr driven means including africtioiiblut'ch for actuating the jaws of the chuck, the improvementwhich comprises automatic means for maintaining said friction clutchengaged with a substantially constant pressure throughout the use fullife of the friction members of said clutch including means to exert aclutch-engaging force means to transmit said forceto said clutch with amechanical advantage, the force exerting means and the forcetransmitting means being so constructed anda'rranged that the mechanicalof the latter increases asthe force ex erted by the former decreases due'to wear oi the friction members of said clutch, whereby theclutch-engaging pressure remains substantially constant so that theclutch transmits 'a' substan tialiy constant torque for actuating thejaws of the chuck and slips when said torque is exceeded.

2. In a machine tool having a chuck and power driven means including a-irictio'n clutch for actuating the "jaws of the chuck, the improvementwhich comprises automatic means for maintaining said friction clutchengaged with a substantially constant pressure throughout the usefullife of the friction members of said clutch including cans to exert aclutch-engaging force and pi to o. lever ineans'to transmit said forceto said clutch with a mechanical advantage, the force exerting means andthe lever means being so constructed and arranged that. theperpendicular distance between the pivot of said lever means and theline of action of the force exerting means in crea es as the forceexerted decreases due to. wear of the friction members of said clutch,whereby maintaining said friction clutch engaged with a substantiallyconstant pressure throughout the useful life of the friction members ofsaid clutch including a compression spring for exerting aclutch-engaging force and pivoted lever meansv to transmit said force tosaid clutch with a mechanical advantage, the spring and the lever meansbeing operatively associated in a manner such that the perpendiculardistance between the pivot of thelatter and the line, of action of theforce exerted by the former increases as the said force decreases due toexpansion of the spring resulting from wear. of the friction members ofsaid clutch, wherebythe clutch-engaging. pressure remains. substantiallyconstant. so, that the clutch is effective to transmit a substantiallyconstant torque forfactuating. the jaws of the chuck and slips when saidtorque is exceeded.

4. In a machine tool having a chuck and power driven means including afriction clutch for tightening the jaws of the chuck, the improvementwhich comprises automatic means for maintaining said friction clutchengaged with a substantially constant predetermined pressure includingmeans to, exert a clutch-engaging force, means to transmit said force tosaid clutch with a mechanical advantage, and adjustable means to opposea selected amount of the force of said force exerting means to provide arange of prede termined clutch engaging pressures, the force exertingmeans and the fierce transmitting means being so eonstructed andarranged that the mechanical, advantage of the latter increases as the oce exe ed b t e a e decrea e due to the Wea of th f icti n member of aClutch whereby the p ta-determined clutch-engaging Pressu e remasubstant al ons 50 that the c utch i efiect ve 'qt a smit a c r on ing.substantially constant predetermined torque fo a t ati he iev j'o he h cn Slips e sa tor ue s exc eded- 5., In a machine tool having a chuck andpower driven mea s nc ud a ictio c tc f i tenins th a s of he. huckimprovement lymp campuses autqma m ns for maintaining said frictionclutch engaged with a substantially. constant predetermined pressureincluding means to exert a clutch-engaging force, means to transmit saidforce to said clutch with a mechanical advantage, and means for exertingan ade justable force upon said transmitting means to oppose a selectedamount of the force of said first-mentioned force-exerting means therebyproviding a range of predetermined clutch-engaging pressures, both ofsaid force exerting means coacting with the force transmitting means ina manner such that the respective products of the mechanical advantagesof'the latter and the forces exerted by. each of the former remainsubstantially constant 'for'. any selected value of said adjustableforce throughout the useful. life of the friction members of the clutch,whereby the predetermined clutch-engaging pressure remains substantiallyconstant so that the clutch isIeffectiv'e. to transmit a corresponding75 substantially constant predetermined torque for actuating the jaws ofthe chuck and slips when said torque is exceeded.

6. In an apparatus of the character described including a supportinghousing and a friction clutch disposed within said housing, the saidfriction clutch comprising interengageable driving and driven frictionmembers rotatable relative to said housing; the improvement whichcomprises a lever of the bell crank type including a force arm and aclutch actuating arm extending at an angle with respect to each other,pivot means pivotally supporting said lever on said housing intermediatesaid arms with the said actuating arm extending transversely of the axesof said friction members, means operatively connecting the clutchactuating arm with said clutch to efiect engagement of said frictionmembers, and means supported by said housing and exerting asubstantially linear force on said force arm in a directionapproximately parallel to the said actuating arm.

7. A friction clutch for transmitting a predetermined torque from adriving to a driven means, the said clutch comprising interengageablefriction members operatively connected to said driving and driven meansrespectively, and means for holding said friction members engaged with aselected predetermined pressure, said last-mentioned means including apivoted three-arm lever, means operatively connecting one arm of saidlever with one of said friction members for moving the latter intoengagement with the other of said friction members, means for exertingforce upon a second arm of said lever to continuously urge said firstarm in a clutch-engaging direction, and means for exerting an adjustableforce on a third arm of said lever in a direction tending to urge saidfirst arm in the opposite direction Whereby the resultingclutch-engaging force exerted by said first arm of said lever may beadjusted to apredetermined value within a given range.

8. A friction clutch for transmitting a predetermined torque from adriving to a driven means, the said clutch comprising interengagingfriction members operatively connected to said driving and driven meansrespectively, and means for holding said friction members engaged, saidlast mentioned means including a pivoted three-arm lever, meansoperatively connecting one arm of said lever with one of said frictionmembers for moving the latter into engagement with the other of saidfriction members, a compression spring adapted to exert force upon asecond arm of said lever to continuously urge said first arm in aclutch-engaging direction, a second compression spring for exerting aforce upon the third arm of said lever in a direction tending to urgesaid first arm in t e opposite direction. and means for adjusting thecompression of said second mentioned spring whereby the resultingclutch-engaging force exerted by said first arm of said lever may beadjusted to a predetermined value within a given range.

9. A friction clutch for transmitting a predetermined torque from adriving to a driven means, the said clutch comprising interengageablefriction members operatively connected to said driving and driven meansrespectively, and means for holding said friction members engagedincluding a pivoted three-arm lever, means operatively connecting onearm of said lever with one of said friction members for moving thelatter into engagement with the other of said friction members, acompression spring for exerting a force upon a second arm of said leverto continuously urge said first arm in clutch engaging direction, asecond compression spring adapted to exert a force on the third arm ofsaid lever in a direction tending to urge said first arm in the oppositedirection, said second and third arms each being provided with a rolleradjacent the outer ends thereof and the lever engaging ends of saidcompression springs each being provided with members having planar facesfor engaging said rollers, and means to adjust the compression of saidsecond mentioned spring to thereby adjust the clutchengaging forceexerted by said first arm.

10. A friction clutch for transmitting a substantially constantpredetermined torque from a driving to a driven means, the said clutchcomprising interengageable friction members operatively connected tosaid driving and driven means respectively, and means for holding saidfriction members engaged with a substantially constant predeterminedpressure, said last-mentioned means including a pivoted three-arm lever,means operatively connecting one arm of said lever with one of saidfriction members for moving the latter into engagement with the other ofsaid friction members, means for exerting a force upon a second arm ofsaid lever for continuously urging said first arm in a, clutch-engagingdirection, means for exerting an adjustable force on the third arm ofsaid lever in a direction tending to urge said first arm in the oppositedirection, the lever and said force exerting means being so constructedand arranged that when the former rocks about its pivot due to wear ofsaid friction members the effective lever arm of said second armincreases as the force exerted thereon decreases and the effective leverarm of the third arm decreases as the force exerted thereon increases,whereby the product of each of said forces by its effective lever armremains substantially constant for any selected value of said adjustableforce so that the friction members of the clutch are held in engagementwith a substantially constant predetermined pressure.

11. A friction clutch for transmitting a substantially constantpredetermined torque from a driving to a driven means, the said clutchcomprising interengageable friction members operatively connected tosaid driving and driven means respectively, and means for holding saidfriction members engaged with a substantially constant predeterminedpressure, said last-mentioned means including a pivoted three-arm lever,means operatively connecting one arm of said lever with one of saidfriction members for moving the latter into engagement with the other ofsaid friction members, a main spring for exerting force upon a secondarm of said lever for continuously urging said first arm in aclutch-engaging direction, a reaction spring for exerting force on thethird arm of said lever in a direction tending to urge said first arm inthe opposite direction, means to adjust the force of said reactionspring to thereby adjust the resulting clutch-engaging force exerted bysaid first arm of said lever to a predetermined value, the said leverand springs being so constructed and arranged that as the lever rocksdue to wear of said friction members resulting alterations in the forcesexerted by said springs are compensated by an inverse change in theeffective lever arms of the said second and third arms of said lever,whereby the resulting clutch-engaging pressure remains substantiallyconstant at the value determined by the adjustment of said reactionspring.

12. A friction clutch of the type defined in claim 11 and in which saidsprings are compression springs each provided with a means having aplanar surface, and said second and third lever arms are each providedwith rollers engaging said planar surfaces, whereby the said rollersremain in contact with said surfaces for all positions of the lever asthe latter rocks due to wear of said friction members.

13. In a machine tool of the type described having a chuck provided withmovable Work-engaging jaws, a wrench spindle adapted to operativelyengage a portion of said chuck to move said jaws to and fromwork-gripping position, reversible power driving means, and operativeconnections includin a, friction clutch having interengaging frictionmembers between said power means and said wrench spindle for rotatingthe latter to move said jaws; the improvement which comprises means forholding said friction members engaged with a substantially constantpredetermined pressure including a pivoted three-arm lever, meansoperatively connecting one arm of said lever with one of said frictionmembers, means for exerting a force upon a second arm of said lever tourge said first arm in a clutch-engaging direction, means for exertingan adjustable force on the third arm of said lever in a directiontending to urge said first arm in the opposite direction, the lever andthe force exerting means being so constructed and arranged that when theformer rocks about its pivot due to wear of said friction members theeffective lever arm of said second arm increases as the force exertedthereon decreases and the effective lever arm of the third arm decreasesas the force exerted thereon increases, whereby the product of each ofsaid forces by its effective lever arm remains substantially constantfor any selected value of said adjustable force so that a range ofsubstantially constant torques are provided for said wrench spindle.

FRED H. BOGART.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,195,286 Snyder Aug. 22, 19161,448,861 Pearson Mar. 20, 1923 1,698,254 Bullard, Jr. Jan. 8, 19291,831,225 Bogart NoV. 10, 1931 2,137,998 Bronander Nov. 29, 1938

